1. Field of the Invention
The present invention relates to a road friction coefficient estimating apparatus for precisely estimating a road friction coefficient in a wide driving range and a vehicle equipped with the road friction coefficient estimating apparatus.
2. Description of the Related Art
In recent years, various control technologies have been proposed and put into practical use with respect to traction controls, braking controls, or torque distribution controls for a vehicle. In these technologies, many apparatuses use a road friction coefficient for calculating a necessary control parameter or correcting thereof, and it is necessary to precisely estimate the road friction coefficient in order to securely perform the control.
Among such technologies for estimating the road friction coefficient, there is the one focused on the fact that magnitude of a self-aligning torque for a slip angle of a tire changes according to the road friction coefficient. For example, Japanese Unexamined Patent Application No.11-287749 discloses a device to estimate the road friction coefficient based on a steering wheel angle and a steering torque.
Further, for example, Japanese Unexamined Patent Application No. 6-221968 discloses a device to estimate the road friction coefficient based on a cornering force of a tire and a self-aligning torque.
However, in the former prior art mentioned above, there is a problem that a front wheel slip angle can not be detected with a steering wheel angle so that conditions enabling the detection of the road friction coefficient are limited, and thereby it is difficult to precisely estimate the road friction coefficient in a wide driving range.
Whereas, in the latter prior art mentioned above, a differential value of a sensor signal such as a differential value of a yaw rate at the time of detecting cornering force is used so that there is a problem of sensor noise, and thereby it is difficult to precisely estimate the road friction coefficient.
In view of the aforementioned, it is an object of the present invention to provide a road friction coefficient estimating apparatus which is able to estimate a road friction coefficient precisely in a wide driving range while reducing noise of a sensor, and a vehicle equipped with the road friction coefficient estimating apparatus.
To attain the object, the road friction coefficient estimating apparatus of the present invention for estimating the road friction coefficient on the road, comprising self-aligning torque detecting means for detecting a self-aligning torque of a steered wheel, steered wheel slip angle detecting means for detecting a slip angle of the steered wheel by inputting a detected value of a vehicle motion parameter to an observer formed by a motion model of a vehicle, and road friction coefficient setting means for setting a road friction coefficient based on the relationship between the self-aligning torque and the steered wheel slip angle.
And the road friction coefficient estimating apparatus of the present invention for estimating the road friction coefficient on the road, comprising a hydraulic power steering device for assisting a steering force by an oil pressure applied to a pair of hydraulic chambers of a power cylinder, oil pressure detecting means for detecting each oil pressure of the pair of hydraulic chambers, self-aligning torque detecting means for calculating a self-aligning torque based on a higher pressure of the pair of hydraulic chambers, steered wheel slip angle detecting means for detecting a slip angle of the steered wheel by inputting a detected value of a vehicle motion parameter to an observer formed by a motion model of a vehicle, and road friction coefficient setting means for setting a road friction coefficient based on the relationship between the self-aligning torque and the steered wheel slip angle.
Also the road friction coefficient estimating apparatus of the present invention for estimating the road friction coefficient on the road, comprising a hydraulic power steering device for assisting a steering force by an oil pressure applied to a pair of hydraulic chambers of a power cylinder, oil pressure detecting means for detecting each oil pressure of the pair of hydraulic chambers, self-aligning torque detecting means for calculating a self-aligning torque based on a difference of pressure in the pair of hydraulic chambers, steered wheel slip angle detecting means for detecting a slip angle of the steered wheel by inputting a detected value of a vehicle motion parameter to an observer formed by a motion model of a vehicle, and road friction coefficient setting means for setting a road friction coefficient based on the relationship between the self-aligning torque and the steered wheel slip angle.
And also, the road friction coefficient estimating apparatus of the present invention for estimating the road friction coefficient on the road, comprising an electric power steering device for assisting a steering force with an electric motor, torsion bar torque detecting means for detecting a torsion bar torque, motor current detecting means for detecting the driving current of the electric motor, self-aligning torque detecting means for calculating a self-aligning torque based on the torsion bar torque and the motor current, steered wheel slip angle detecting means for detecting a slip angle of the steered wheel by inputting a detected value of a vehicle motion parameter to an observer formed by a motion model of a vehicle, and road friction coefficient setting means for setting a road friction coefficient based on the relationship between the self-aligning torque and the steered wheel slip angle.
The above and other objects, features and advantages of the invention will become more clearly understood from the following description when taken in conjunction with the accompanying drawings.